EP 77. Brain imaging findings in idiopathic REM sleep behavior disorder (RBD) – Potential markers for neurodegeneration –

Abstract

Objectives Idiopathic REM sleep behavior disorder (RBD) is a parasomnia characterized by the loss of physiological atonia of skeletal muscles during dream sleep. This leads to enactment of dream content with nocturnal behavior such as flailing of the arms, kicking and/or vocalization ( Boeve, 2010 ). RBD may be the initial manifestation of neurodegenerative α -synucleinopathies (Parkinson’s disease [PD], Parkinson’s disease dementia [PDD], dementia with Lewy bodies [DLB], multiple system atrophy [MSA]) ( Boeve, 2010 , Postuma et al., 2009 ). Nevertheless, individual prognoses concerning the type of subsequent disease and time of phenoconversion are still challenging. By concentrating recent brain imaging findings on the radionuclide imaging techniques of single photon emission computerized tomography (SPECT) and positron emission tomography (PET), structural and functional magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS) and transcranial sonography (TCS) in RBD, we aimed to identify potential neuroimaging markers enabling a more accurate prediction of neurodegenerative processes in this disease. Methods We ran electronic searches for English peer-reviewed journal articles indexed in the PubMed database using the following keywords: “(REM sleep behavior disorder OR RBD) AND (imaging OR neuroimaging OR TCS OR PET OR SPECT OR MRI OR MRS)”. In addition, we browsed through reference lists and published reviews focusing on this or similar topics. We only considered studies assessing the human brain. Furthermore, solely studies that addressed idiopathic RBD without comorbid mental disorders, neurologic or neurodegenerative diseases were included, unless these studies compared RBD patients additionally suffering from comorbidities to patients with idiopathic RBD. Results Overall, PET and SPECT (n = 20 studies) are of best prognostic value for the identification of RBD patients being at risk to phenoconvert. Moreover, these techniques are useful in the early or even premanifest differential diagnosis of emerging α -synucleinopathies such as PD, DLB and MSA ( Fig. 1 ). Conventional structural MRI (n = 7 studies) so far mostly revealed unspecific findings in RBD. In contrast, the few studies focusing on diffusion-weighted structural MRI (n = 2 studies), functional resting-state MRI (n = 1 study), imaging of brain iron content (n = 1 study) and phosphor and proton MRS (n = 2 studies) provided promising results for the early identification of progressive neurodegeneration in RBD patients. Lastly, although sensitivity is limited, TCS (n = 7 studies) is helpful in the identification of RBD patients being at a specific risk for the development of PD ( Fig. 1 ). Conclusion While PET, SPECT and TCS already offer sensitive imaging markers to identify RBD patients at risk for progressive neurodegeneration, studies focusing on MRI and MRS are more limited. Further imaging research applying multimodal approaches is encouraged to enhance accuracy of prognosis. Additionally, more longitudinal studies are warranted to validate findings from cross-sectional studies on RBD progression and risk of subsequent phenoconversion. Aside from enabling reliable prognoses on a single-subject-level in the near future, this might give further insight into RBD pathophysiology, and finally augment the development of intervention strategies and disease-modifying therapies.